在下面的代码中，我必须限定equal()调用（否则我会得到“对重载函数的模糊调用”），但可以调用 unqualified find()。有什么不同？
#include <iterator>
#include <vector>
#include <iostream>
using std::vector;
using std::cout;
using std::endl;
// Test whether the elements in two ranges are equal.
// Compares the elements in the range [b,e) with those in the range
// beginning at d, and returns true if all of the elements in both ranges match.
template <class InIter1, class InIter2>
bool equal(InIter1 b, InIter1 e, InIter2 d)
{
cout << "My equal()" << endl;
while (b != e)
if ((*b++) != (*d++))
return false;
return true;
}
// Returns an iterator to the first element in the range [b,e)
// that compares equal to t. If no such element is found, the function returns last.
template <class InIter, class T>
InIter find( InIter b, InIter e, const T& t )
{
cout << "My find()" << endl;
while (b != e) {
if ( *b == t )
return b;
b++;
}
return e;
}
/* "Accelerated C++", ex. 8.2 */
int main()
{
static const int arr[] = {8, 7, 15, 21, 30};
vector<int> vec(arr, arr + sizeof(arr) / sizeof(arr[0]) );
cout << "equal() result: " << ::equal(vec.begin(), vec.end(), vec.rbegin()) << endl;
vector<int>::iterator iter = find(vec.begin(), vec.end(), 21);
if (iter == vec.end())
cout << "did not find()" << endl;
else
cout << "find() result: " << *iter << endl;
return 0;
}
我认为它与参数相关查找有关（请参阅this question），但仍然不明白为什么这两个调用不同。